The invention relates to a bolt for fastening two structural members together and more particularly to a bolt having an integral locking member which may be deformed to fit with one of the structural members in order to prevent untorquing of the bolt.
In the past two decades, the commercial nuclear power industry has become concerned that bolts originally provided in reactor pressure vessels for fastening internal structural members such as plates, tubes and the like together may untorque or become subject to corrosion cracking after years of exposure to irradiation, high temperatures, high pressures, fluid flow induced vibrations and high velocity water and/or steam flows. Accordingly, the operators of some plants have tack welded the heads of the bolts to the structural members in several applications. However, welding must be very carefully performed under difficult physical conditions in order to minimize stresses and compositional variations in the weld and heat effected zones which may result in welds susceptible to stress corrosion cracking.
Replacement bolts for fastening reactor vessel internals together have been designed with locking members which are deformed (e.g., by crimping) to engage recesses machined into the sidewalls of countersunk bolt holes in the structural members for restricting the bolts. See, e.g.: U.S. Pat. No. 4,683,108 to Balog, U.S. Pat. No. 4,711,760 to Blaushild and U.S. Pat. No. 5,771,266 to Fabris which show a bolt with a separate locking member for fastening a baffle plate and a former plate in the core barrel of a pressure vessel in a pressurized water reactor; and a KWU Service Report dated September 1997 by Christian Hillrichs entitled "Replacement of Bolts in RPV Internals" which shows a bolt with an integral locking member for fastening a core shroud and a core support in a pressure vessel in a boiling water reactor. Such bolts are on the order of one half inch to about five eight inch or more in diameter by about two inches or more in length. Also, they generally are fabricated of an austenitic stainless steel (such as Type 316 or Type 347) or of a nickel alloy (such as alloy X-750). These replacement bolts may installed and deformed in submerged shutdown reactor vessels with tooling and equipment similar to that shown by the KWU Service Report and by U.S. Pat. No. 4,991,280 to Reimer et al.
The nuclear power industry prefers the use of integral replacement bolts rather than two piece bolts in order to simplify the bolt installation process. However, the locking members of replacement bolts must be designed so that they may be readily deformed by existing tooling. While integral replacement bolt designs have been successfully installed and used to fasten internal structural members of reactor pressure vessels, the nuclear power industry is concerned that deformed regions of the locking members may themselves be susceptible to stress corrosion cracking.